The present invention relates to a single-cylinder circular machine with improved platen actuation, in particular for manufacturing socks, stockings and the like.
As is known, single-cylinder circular machines for manufacturing socks, stockings and the like are generally constituted by a vertically arranged needle cylinder which can be actuated with a rotary motion about its own axis and supports a plurality of needles which are accommodated in axial grooves defined on its outer surface. Said needles are actuated individually by means of cams which are arranged around the needle cylinder and define paths which can be followed, during the rotation of the needle cylinder with respect to said cams, by a needle heel which protrudes from the needle cylinder.
The paths defined by said cams have rising portions and descending portions in order to cause the reciprocating movement of the needles along the grooves of the needle cylinder and to make said needles take up the threads which are fed thereto and form the stitches which compose the sock or stocking.
A platen is coaxially arranged above the needle cylinder; radial grooves are defined on its upper face and slidingly accommodate a plurality of needles or hooks, depending on the type of machine or product to be manufactured.
The number of needles or hooks of the platen is equal to the number of needles provided in the needle cylinder, and when the needles or hooks of the platen knit, the cylinder and the platen must be rotated in a mutually rigid manner, with each hook or needle of the platen arranged between two contiguous needles of the cylinder in order to avoid mutual interference.
Furthermore, in many types of machine the platen is provided, on its upper face, with a coaxial circular cutter which is used to cut the threads when their knitting ends. More particularly, at the end of the knitting of a thread, said thread remains engaged with the last needle which knitted it and is lowered into the needle cylinder; the thread is taken up by a tooth of the cutter, which rotates together with the platen and the needle cylinder, and is moved to a fixed abutment, termed knife, which cooperates with the cutter in order to cut the thread.
The platen is generally rotated by means of a gear connection to the transmission which actuates the needle cylinder, so as to avoid angular displacements between the cylinder and the platen.
The U.S. Pat. No. 4.580.420 granted Apr. 8, 1986, discloses a circular machine for manufacturing socks wherein the rotational connection between the platen and the needle cylinder is obtained by means of an oscillating lever which is pivoted to the platen with its upper end and extends inside the needle cylinder. The lower end of said lever can be controllably engaged, by using its ability to oscillate, with an axial groove defined on the inner surface of the needle cylinder, so that the platen is rotated by the needle cylinder. Said rod is disengaged from the needle cylinder only at the end of the forming of the sock in order to allow its outward unloading.
Although this solution eliminates the gear transmission for the actuation of the platen, it has some disadvantages.
In fact, since the sock descends around the rod connecting the platen to the cylinder during knitting, the rod must have an adequate length. Due to this fact, the torsional deformability of the rod can cause unwanted displacements between the cylinder and the platen, with the risk of interference between the needles of the cylinder and the hooks of the platen. Furthermore, since the rod is in any case generally shorter than the product, folds or creases occur in the sock and, with some types of thread, remain even after ironing it. Another disadvantage is a reduction in the efficiency of the pneumatic aspiration to which the sock is subjected during manufacture.
In other types of machine, the connection between the needle cylinder and the platen can be defined as mixed. In fact, a rod of the type described in the above mentioned patent is provided, but it is shorter in order to provide a precise connection between cylinder and platen; furthermore, when said connection is not used, the platen is rotated, with a speed which is substantially equal to that of the cylinder, by means of an independent motor which is connected to the platen by means of a transmission.
In this case, the precision connection between platen and cylinder is used generally only at the beginning of the knitting of the sock, i.e. during the knitting of the trimming, when the actuation of the hooks is required, whereas when the hooks do not knit, the rotation of the platen and the possibility to use the cutter to cut the threads are allowed by the independent motor.
However, even this solution is not free from disadvantages. In fact, higher costs arise with respect to the previously described solution; said costs are mainly due to the cost of the independent motor and to additional costs for the higher energy consumption required for its actuation. Furthermore, the presence of the motor arranged above and laterally to the platen constitutes an unwanted bulk in the region intended for supporting the spools of thread which feed the machine, and makes it difficult to raise the platen.
In any case, problems also occur in connecting the needle cylinder and the platen with gears, since the plays among the various gears can alter the correct mutual arrangement of needle cylinder and platen.